DE4323956C1 - Fusion dowel for vertebrae - Google Patents

Abstract

The invention describes a fusion dowel (1) for vertebrae which is used to fuse two adjacent vertebrae of the human spine. Essentially, it comprises a sleeve (2) which is slit lengthwise over essentially two thirds of its length by at least two slots (3) and is thus subdivided into at least two segments which can be spread apart. The sleeve (2) is penetrated by a screw (5) inserted in the sleeve (2) on the proximal front face thereof which is closed except for a bore (6) for the screw (5). A nut (7) having a circular cross-section and an outer surface (8) that widens conically toward the open sleeve end starting from a cylindrical part (7') is placed in the distal end of the sleeve (2). The diameter of the cylindrical section (7') roughly corresponds to the internal diameter of the sleeve (2). The screw (5) can be connected to the nut (7) by screwing. On continuous screwing movement the region of the conically widening outer surface (8) of the nut (7) reaches the front opening of the sleeve (2) and ensures spreading of the wall segments of the sleeve (2) from this point onwards. <IMAGE>

Description

The invention relates to a vertebral body fusion anchor according to the Preamble of claim 1 for bony fusion two adjacent vertebral bodies of the human spine.

Vertebral body implants are generally known for the fusion of two vertebral bodies. The so-called Keystone implant is classic, for example. More recently Such implants are known for example from DE 40 12 622 C1 and DE 91 01 603 U1. The implants described therein are very good advantageous, but primarily intended for applications in which whole Vertebral bodies have to be partially resected and replaced. You are therefore from its dimension alone quite expansive and mechanically complicated, what however, is also justified in the application cases intended for them. However, the situation is different with smaller defects of the vertebral body or the intervertebral disc in between. In contrast to indication cases, in which implants of the type described above are used, medically quite simple cases, it is not indicated per se, with such large Surgical implants to remedy the situation. Of course, this is where it plays medical philosophy mattered as much as possible in the body's own parts Leave the body and remove as little damaged parts of the body as necessary.

A spinal implant has become known from EP-0 260 044 A1. According to one embodiment, there is essentially one form cylindrical body in two parts from two half-shells. Inside them is a threaded spindle with opposing threads, on which two Cams are screwed on. The two cams are not under tension Condition of the implant housed in suitably designed pockets in the two cylinder halves. On a rotation of the threaded spindle for  Clamping the implant in the spine will remove these cams from the said pockets pushed out so that the two halves of the cylindrical Body are spread apart. So it finds one Parallel displacement of the vertebral body takes place on which the two cylinder halves issue.

However, it turns out to be problematic that in the case of the attachment of a Hole or a channel in a vertebral body that has not yet been extracted The implant can be placed there, but if the threaded spindle is rotated so that the two cylinder halves are parallel to each other remove, the implant is only held in place by a press fit Spine. At the entrance of the channel or the hole drilled there is the same cross-section for the implant as at the end of the same, namely an oval cross section. Due to daily stress on the spine Life cannot be ruled out that the press fit of the implant is relaxed and the patient the risk of slipping out Implant grows from the hole or from the channel. this is not acceptable.

According to a later proposal according to WO 92/14423, in which also mentioned implant is mentioned, slipping out of the Canal in the vertebral body tries to counteract it by the implant after insertion into the channel, its cross section enlarged in the middle becomes. At the beginning and at the end of the canal or borehole there are smallest cross sections, while the cross section of the implant after the Implantation and clamping in the middle is greatest. It is true that the Slipping out is effectively counteracted. Being a disadvantage however, considered that the largest expansion or spread of the Implant is not made at the actual place of occurrence, so to speak is, but far behind. The place where an implant is Should have therapeutic effect, is the transition area from bony Material of a vertebral body to the intervertebral disc, which in the indexed  Operation and use of such an implant is damaged. In the border area Care should be taken between bony material and the damaged spine to bear that the spread is greatest in this area. This can to do none of the known implants.

Against this background, it is the object of the present invention Implant for the bony fixation of two adjacent vertebral bodies Human spine indicate which of these vertebral bodies is permanent connects with each other and at the same time for the maximum spread of the neighboring vertebral bodies in the area of the interface between bony Material and the material of the intervertebral disc ensures.

Starting from the implant according to the mentioned WO 92/14423, this is Task by the implant with the characterizing features of claim 1 solved. Further advantageous configurations result from the Subclaims. Accordingly, it is proposed to use the implant as a kind of dowel to train. How the implant is made according to the aforementioned document this from a sleeve and a screw penetrating the sleeve, which on the except for a hole for the screw closed proximal end face the sleeve is inserted into this. According to the invention it is now provided that at least two in the sleeve from its distal end to the proximal end essentially 2/3 of their length slots and one with the Screw screwable nut are provided, which from the distal side in the Sleeve engages, the nut being circular in cross section and starting from a cylindrical part a conical to the open sleeve end has widening lateral surface and the diameter of the cylindrical Section corresponds approximately to the inner diameter of the sleeve. That causes, that the cylindrical section can first be guided in the sleeve.

As you can see, when you tighten the screw further, it becomes special trained mother pulled even further into the sleeve. So is the mother pulled far into the sleeve, that now the conical  widening lateral surface is present on the distal face of the sleeve, and will the screw is turned further, the sleeve is pulled into it Widening of the wall segments of the sleeve. This brings the well-known Locking effect of a dowel.

In contrast to the generic publication WO 92/14423, the Vertebral body fusion dowel according to the invention after tensioning a trapezoidal or V-shaped shape with the maximum spread at its distal end is achieved, namely exactly where the bore or the channel in the Vertebral bodies in the border area to the intervertebral disc material ends.

It is clear that the mother must be made of a correspondingly harder material, to expand the body-compatible metal of the sleeve.

The primary fixation achieved by widening the wall segments is the same a press fit. For a permanent secondary fixation and thus a permanent one Fusion of both vertebrae is advantageously provided that the outer Shell surface of the sleeve with a three-dimensional open-mesh Spatial network structure is documented in which bone trapezoids  can wax in and thus ensure a permanent hold. The making of a Such a spatial network structure results, for example, from DE 41 06 971 C1.

In order to avoid unintentional loosening of the nut from the screw preferably provided that the nut by means of an anti-rotation lock is secured. This anti-rotation device can, for example a radial groove in the disc and a snap ring engaging therein.

The handling of the implant according to the invention is thereby made clear in situ simplified that, according to an advantageous embodiment, one of the longitudinal slots in the Sleeve is formed in the distal region as a guide groove, for one at the Bolt attached to act as an anti-rotation lock. This will make the mother prevented from turning instead of an expansion of the wall segments.

The invention is based on an embodiment according to the drawing figures explained in more detail. Here shows

Fig. 1 is a side view of the inventive implant,

Fig. 2 is a sectional view of the implant of Fig. 1, and

Fig. 3 seen a plan view of the implant of Figs. 1 and 2 from the right.

In the following, identical parts are provided with the same reference symbols.

1 provides a first overview . The vertebral body fusion anchor 1 shown therein consists of a sleeve 2 , which is shown here as having a three-dimensional open-mesh spatial network structure 4 . In the present case, the sleeve 2 has four longitudinal slots 3 ( FIG. 3), which in the exemplary embodiment shown extend four-fifths over their length. One of the three slots 3 is expanded in the distal region to a guide groove 10 , in which a bolt 11 is guided, which is connected to the nut 7, which is pushed into the distal end of the sleeve and with which the screw 5 passing through the sleeve 2 is screwed is. The proximal side of the sleeve 2 (on the left in FIG. 2) is closed except for the through-hole 6 for the screw 5 . The nut 7 has a cylindrical part 7 ' , the diameter of which corresponds approximately to the inside diameter of the sleeve 2 . This cylindrical part 7 'of the nut 7 joins to the distal end a section with a conically widening lateral surface 8 .

The dowel works as follows:
After a suitable cutout has been made in the two vertebral bodies to be fused, the pre-assembled, approximately cylindrical dowel with nut 7 and screw 5 is placed in the cutout and then the screw 5 is actuated by means of a screwdriver, whereupon the sleeve 7 is pulled further into the inside of the sleeve . If the area with conically widening lateral surface 8 reaches the end face of the sleeve, further rotation of the screw causes the wall elements of the sleeve to spread apart. The dowel spreads and ensures the fusing effect.

After the implantation, bone trapezoids grow into the three-dimensional open-mesh spatial network structure 4 and thus ensure stable long-term fixation or fusion.

Claims (4)

1. vertebral body fusion dowel ( 1 ), consisting of a sleeve ( 2 ) and a screw penetrating the sleeve, which is inserted into the screw on the proximal end face of the sleeve, which is closed except for a through-hole ( 6 ), characterized by at least two in the Sleeve ( 2 ) from its distal end to the proximal end via slots ( 3 ) running essentially 2/3 of its length, and a nut ( 7 ) which can be screwed to the screw ( 5 ) and which penetrates into the sleeve ( 2 ) from the distal side. engages, the nut ( 7 ) having a circular cross-section and, starting from a cylindrical part ( 7 ' ), a jacket surface ( 8 ) which widens conically towards the open sleeve end and the diameter of the cylindrical section ( 7' ) roughly corresponds to the inside diameter of the sleeve ( 2 ) corresponds. 2. vertebral body fusion dowel according to claim 1, wherein the outer lateral surface of the sleeve ( 2 ) is covered with a three-dimensional open-mesh spatial network structure ( 4 ). 3. vertebral body fusion dowel according to claim 1 or 2, wherein the nut ( 7 ) is secured against twisting off the screw ( 5 ) by means of an anti-rotation device ( 9 ). 4. vertebral body fusion dowel according to one of claims 1 to 3, wherein one of the slots ( 3 ) in the distal region is designed as a guide groove ( 10 ) for a on the nut ( 7 ), acting as an anti-rotation bolt ( 11 ).